The combination of a chronic drug self-administration preparation along with a refined choice methodology permits a research program which addresses issues concerning mechanisms of drug reinforcement in baboon subjects. Research in three inter-related areas will be undertaken: 1) Evaluation of pharmacologic and environmental factors which may interact with heroin or cocaine reinforcement. 2) Evaluation of relative reinforcing properties of cocaine, various opiates and various barbiturates. 3) Evaluation of procedures for eliminating heroin dependence, including administration of methadone, administration of the narcotic antagonist naloxone.